High Intelligibility Classrooms
There are classrooms and there are high intelligibility
classrooms. Who gets high intelligibility classrooms?
- Hearing and learning disabled
- Language Arts
- Vocabulary oriented classroom
- Music and practice rooms
- TV learning centers
- Multilingual population classrooms
- Larger classrooms and lecture halls
Normal classrooms are quite reverberant. This is
due to the hygiene tradition of public spaces. Familiar speech can
be more easily understood in a semi-reverberant space than is unfamiliar
speech. For example, instructions in a gym class will contain almost
no new words. The familiar context and expectation of word sequences
will help the listener hear, actually guess/expect what is being
Learning a foreign language in a gym would be almost
impossible because there is no backlog of experience that can lead
to expected word sequences. This applies also to classes steeped
in new vocabulary such as biology.
Children who are hearing or learning disabled are
much more easily distracted by the reverberation of sound. They
seem to fall short in their ability to discriminate between the
intentional, direct sounds from the teacher and the time delayed
cacophony of these same sounds after they have undergone multiple
reflections within the room.
For bilingual students, the classroom language is
their adopted language. They are not used to the context of this
second language and therefore have reduced confidence in expectation
of word sequences. They cannot hear through classroom noise as easily
as primary language based students. These second language students
operate with a learning disadvantage due to poor room acoustics.
Larger classrooms and lecture halls lose yet another
cue factor that does exist and helps students to "see through" noisy,
reverberant classrooms. This is the visual cue. In small classrooms,
the student can focus on the mouthing of words to help understanding.
Over long distances, this lip reading factor disappears leaving
only body language as support for sentence detail.
Even normal sized classrooms suffer from the loss
of visual cues. In the back of the room, reverberant levels are
greatest and the direct signal is weakest. The distance from student
to teacher is greatest and visual cues are weakest. This is complicated
as the heads of other students are often in the way. We can next
add or factor in the general attitude of the students who choose
to sit in the back of the room. Accompanying all this is the shuffle
and murmur or "self noise" noise levels. There is little wonder
these far field student positions will be accompanied by lower levels
of attentiveness. The conglomeration of these effects serves to
suggest that wide shallow classrooms ought to be preferred over
long narrow classrooms.
Music practice rooms are like language classrooms
except students anticipate not their own voice but the voice of
their instrument. Still their ears must synchronize their own sounds
to those of the ensemble and the conductor's expectations. Excessively
reverberant spaces isolate the student. Rather than perceiving themselves
set into a teamwork relationship with other members, they find themselves
playing against a wall of sound, the reverberant sound field. They
cannot practice and develop the skill of hearing themselves within
the context of other individual instruments if they cannot separate
out to render distinct the other instruments from the reverberant
Another area for enhanced intelligibility is the
rapidly growing TV monitor education format. In this setting there
often is no visual available for the student, no lip movement and
no body language need be present. Additionally, the fixed sound
source associated with TV sets is very different from the ever moving
source of a live teacher. Audio speakers have sound dispersion characteristics,
high frequencies radiate forward while the lower tones radiate equally
in all directions. The human voice is the same in this regard. The
difference is that a person continuously moves head and body. The
higher frequency beamy part of the soundfield is always being cast
about, not so with the fixed position TV monitor. With the lower
registers, a fixed TV or audio monitor will acoustically couple
very easily to room resonances which establish those monotonous
drone tones and room boom that accompanies the presentation. Sound
is quite different with an animated source, where every movement
changes the coupling to room resonance and so the coloration is
continuously changing and much less dreary. Acoustic control of
the walls and ceiling near the TV monitor is very important in developing
a comfortable fit for student audition.
I have reviewed the more important consequence of
classroom cacophony. I am confident you are fundamentally aware
of these factors but I must say that architects in general are one
to two decades behind most current practices in acoustics. It is
imperative that any school plan for the 90's include considerations
for the intelligibility factor.
The architect is presently familiar with absorption
coefficients and decay rate criteria for sound in various types
of spaces. The sound system and acoustic engineers have testing
equipment such as sound level meters, octave band and RT-60 analyzers
to support this level of understanding.
As with all science and practice, sophistication
and experience produce new levels of understanding and competency
in manipulating the variables. So it is with psychoacoustics. And
the emergent topic these days is intelligibility. There already
exists intelligibility standards and intelligibility testing equipment.
Crown International (U.S) makes one piece of gear and B & K (Denmark)
makes another. Most of the top acoustic engineers and sound system
designers already have this equipment and use it regularly in setting
up churches, halls, or any area of amplified sound. The technology
can easily be extended into the acoustics of the classroom.
The important point to remember is that different
intelligibility standards will go with different applications. Some
of this criteria for the classroom no doubt has yet to be developed.